The UKHSA predicts that Omicron will become the dominant strain in the UK by the middle of December, accounting for more than 50% of all cases of COVID-19

Production line for COVID-19 vaccine vials

The Omicron variant of severe acute respiratory syndrome coronavirus 2 is continuing rapid growth in all areas of England, new data from the UK Health Security Agency (UKHSA) show.

If Omicron continues to grow at the present rate, the variant will become the dominant strain, accounting for more than 50% of all COVID-19 infections in the UK by the middle of December, the Agency said in a technical briefing.

It said that current projections suggest that the UK could see more than a million infections by the end of the month.

Vaccine effectiveness 

The briefing also included an analysis of vaccine effectiveness against the Omicron variant compared with the currently predominant Delta variant.

A preliminary analysis suggests that the AstraZeneca/Oxford University and Pfizer/BioNTech vaccines provide much lower levels of protection against symptomatic infection with the Omicron variant than with the Delta variant.

However, these preliminary data suggest that, in the early period after a booster dose, vaccine effectiveness could confer around 70–75% protection.

The UKHSA says that the data should be treated with caution because they were based on just 581 people with confirmed Omicron.

In particular, the early analysis of two doses of the AstraZeneca/Oxford University vaccine may be unreliable, largely because it was given to an older population with more comorbidities than the Pfizer/BioNTech vaccine.

The UKHSA says that, although it will be several weeks before vaccine effectiveness against severe disease from Omicron is known, it is likely to be significantly higher than protection against symptomatic disease.

None of the people infected with Omicron since it was first detected in the UK on 28 November 2021 is known to have been hospitalised or to have died, the Agency said.

Take up booster when eligible

Dr Mary Ramsay, Head of Immunisation at the UKHSA, said: ‘These early estimates should be treated with caution, but they indicate that a few months after the second jab, there is a greater risk of catching the Omicron variant compared to Delta strain.

‘The data suggests this risk is significantly reduced following a booster vaccine, so I urge everyone to take up their booster when eligible.

‘We expect the vaccines to show higher protection against the serious complications of COVID-19, so if you haven’t yet had your first two doses please book an appointment straight away.’

Commenting on the technical briefing to the Science Media Centre, Jonathan Ball, Professor of Molecular Virology at the University of Nottingham, said: ‘Few expected vaccines to prevent against infection, or even mild disease—at least not for the mid to long term. 

‘What is important is to understand how the vaccines, especially after the booster dose, protect from serious disease. As the report points out, you can only get that information from real-life experience’, he said. ‘Yes, the amount of antibody killing measured in the lab is lower, but we still don’t understand what that means. Importantly, the booster reinstates much of that killing effect, and we also have T cells to throw into the mix.’

The latest UK data show that 89% of people in the UK aged 12 years and older have had a first dose of vaccine, and 81.2% have had a second dose, as of Thursday 9 December 2021.

Booster doses have been given to 38.6% of the eligible population, with 469,479 people receiving a booster on 9 December.

More than 620,000 people have booked their boosters over the last 2 days after those aged 40 years and older were told that they were able to make appointments 3 months after their second dose.

This article originally appeared on Medscape, part of the Medscape Professional Network.

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